The invention relates to improvements in hydrokinetic torque converters. More particularly, the invention relates to improvements in hydrokinetic torque converters of the type wherein a housing containing a body of oil or another suitable hydraulic fluid is rotatable by the output element of a prime mover (e.g., by the camshaft or crankshaft of an internal combustion engine in the power train of a motor vehicle), a pump is confined in and rotates with the housing, a turbine is disposed in and is rotatable with and relative to the housing, a rotary output member (such as the input shaft of a change-speed transmission in the power train of the motor vehicle) is arranged to rotate with the turbine, and a fluid-operated bypass or lockup clutch is installed in the housing and is engageable to transmit torque from the housing directly to the turbine rather than by way of the pump and the body of fluid in the housing.
As a rule, the bypass clutch of a hydrokinetic torque converter employs a bypass member in the form of a piston which is movable axially of the housing to thus engage or disengage the clutch. When the bypass clutch is engaged, the piston bears upon a wall of the housing and transmits torque to the turbine, i.e., to the output member of the torque converter (e.g., to a hub which forms part of or is non-rotatably connected with the turbine as well as with the output member of the torque converter).
The piston of the bypass clutch is installed between two chambers of the housing, namely a first chamber between one side of the piston and the aforementioned wall of the housing, and a second chamber which is located between the other side of the piston and the turbine. The first chamber can receive or discharge pressurized fluid by way of an axial passage in the output member, and the second chamber can receive or discharge fluid by way of a second passage, e.g., an annular passage between the output member and a hollow shaft which surrounds the output member and can carry a stator disposed in the housing between the pump and the turbine.
Hydrokinetic torque converters are becoming increasingly popular in the power trains of motor vehicles, especially in the power trains of passenger cars, because they contribute to the comfort of the occupant or occupants. The purpose of the bypass clutch is to avoid losses in energy during those stages of operation of a motor vehicle which do not necessitate a shifting into a different gear of a transmission which is connected with the output member of the torque converter. Energy losses can develop as a result of slip between the pump and the turbine when the turbine receives torque by way of the body of fluid in the rotary housing of the torque converter. Thus, the slip is eliminated as soon as the bypass clutch is engaged before the aforementioned bypass member (piston) enables the turbine to bypass the pump, i.e., the turbine then receives torque directly from the rotary housing of the torque converter. Those surfaces of the piston and the housing wall which are in frictional contact with each other when the bypass clutch is engaged are, or can be, cooled by streamlets of fluid flowing from one of the chambers, in channels or grooves provided in the friction surface(s) of the piston and/or the wall, and into the other chamber of the housing. For example, a suitable coolant can flow from the second chamber, through the channel(s) in the torque transmitting friction surface(s) of the piston and/or the wall, through the first chamber and into the axial passage of the output member.
Reference may be had, for example, to commonly owned U.S. Pat. No. 5,501,309 granted Mar. 26, 1996 to Ernst Walth et al. for "HYDROKINETIC TORQUE CONVERTER WITH LOCKUP CLUTCH" and/or to commonly owned U.S. Pat. No. 5,782,327 granted Jul. 21, 1998 to Dieter Otto et al. for "HYDROKINETIC TORQUE CONVERTER AND LOCKUP CLUTCH THEREFOR". The disclosures of these patents, of the published German patent application Ser. No. 44 23 640 A1, as well as of all other patents and/or patent applications identified in this specification are incorporated herein by reference.
If the fluid which flows from the first chamber of the housing into the axial passage of the output member of the torque converter encounters a pronounced resistance to the flow into the axial passage, the pressure of fluid in the first chamber rises with attendant reduction or weakening of frictional engagement between the piston of the bypass clutch and the wall of the housing of the torque converter. In other words, the magnitude of the torque which can be transmitted by the engaged bypass clutch has a low or relatively low upper limit.
A proposal to increase the maximum torque which can be transmitted by the engaged bypass clutch in the housing of a hydrokinetic torque converter is disclosed in the aforementioned published German patent application Ser. No. 44 23 640 A1. It is proposed to provide several discrete conduits which can convey hydraulic fluid from the first chamber of the housing into the axial passage of the output member of the torque converter. A drawback of such proposal is that the conduits contribute to the bulk and cost of the torque converter. Furthermore, it has been found that the plural conduits offer a pronounced resistance to the flow of a hydraulic fluid therethrough, i.e., their ability to eliminate or reduce the adverse influence of the aforediscussed conventional modes of conveying fluid from the first chamber of the housing into the axial passage of the output member is nil or negligible at best.